1. Field of the Invention
The systems and methods of this invention generally relate to communication systems. In particular, the systems and methods of this invention relate to Orthogonal Frequency Division Multiplexing (OFDM) communication systems, methods and protocols.
2. Description of Related Art
The IEEE 802.11a and 802.11g standards for wireless LANs, which are incorporated herein by reference in their entirety, herein after referred to as 803.11a/g, specify wireless local area network communication systems in the 5 GHz and 2.4 GHz bands. These standards specify the use of OFDM as the modulation method used for communication. OFDM is a multicarrier modulation scheme that performs well in wireless communication channels. The 802.11a/g standards provide data rates of 6, 9, 12, 18, 24, 36, 48 and 54 Mbps. Different data rates are achieved by transmitting different, but constant, numbers of bits on all carriers in the multicarrier system and by operating at different coding rates. Table 1 below illustrates the coding rate and bits per subcarrier for each data rate for an exemplary 802.11a/g transceiver.
TABLE 1DATARATEBits per Subcarrier(Mbps)Coding Rate (R)(N_BPSC)6½19¾112½218¾224½436¾448⅔654¾6
In order to determine the appropriate transmission data rate, the 802.11a/g transmitter uses a trial and error method of transmitting at various data rates, starting with, for example, the highest or last successful transmission rate, and waits for a positive acknowledgement indication from the receiver that the packet was successfully received. This simple positive acknowledgment indication method is used to optimize communications in conventional 802.11a based wireless systems.